1. Field of the Invention
The present invention relates to a container for accommodating a coil comprising a functional optical fiber, and to an optical fiber module having the container.
2. Description of the Background Arts
Optical fiber modules comprise, for example, a box-shaped container, a functional optical fiber wound in a coil shape and accommodated in a container, and an optical connection terminal for establishing a connection to an external optical device provided to an end of the functional fiber. The functional optical fiber may be a dispersion compensating fiber (DCF), an optical amplifying fiber, a highly nonlinear fiber (HNLF), or the like. The optical fiber coil comprising the functional fiber is commonly accommodated in a container in a configuration wherein the optical fiber coil is wound around a bobbin, or is covered in a resin. The optical connection terminal is connected to input/output ends of the optical fiber coil through an optical fiber that has an excess length part.
FIGS. 7A and 7B are perspective views of conventional optical fiber modules. An optical fiber module 101 as shown in FIG. 7A is disclosed in Japanese Laid-Open Patent Application Publication No. 2003-4951. The optical fiber module 101 has an optical connection terminal (connection adapter 103) for connecting an optical fiber cord on a front wall part of a container 102. An optical connector provided to an end of the optical fiber that has an excess length part is inserted into the connection adapter 103.
An optical fiber module 201 as shown in FIG. 7B is disclosed in Japanese Laid-Open Patent Application Publication No. 2006-201662. The optical fiber module 201 has a pigtail optical fiber 205 in a manner in which it can be drawn in and out via a hole 204 provided to a front wall part of a container 202. The inner end of the pigtail optical fiber 205 is fusion-spliced to input/output ends of the coil comprising the functional optical fiber. An optical connection terminal (optical connector 206) is attached to an end that is drawn out to the exterior. An excess length portion of the pigtail optical fiber 205 is extendably accommodated on an excess-length takeup reel or the like inside the container 202 so that the length of the pigtail optical fiber 205 drawn out is adjusted in association with the connection distance relative to an exterior optical device and is maintained.
It is necessary to use an optical fiber cord that has an optical connector on both ends in order to connect the optical fiber module 101 to the external optical device. This increases the number of connection points using optical connectors, and leads to a problem having large connection loss. In addition, when optical damage leads to malfunctioning of the optical connection terminals, it is difficult to exchange it.
The fiber module 201 can be connected directly to the external optical device through the pigtail optical fiber, and increment of connection losses due to the optical connector can be prevented. In addition, when optical damage causes a malfunction to occur in the optical connection terminals, it is easy to exchange it. However, the mechanism accommodating the excess length portion is complex. Furthermore, the bend radius tends to be relatively small, and a risk is presented that the pigtail optical fiber will be damaged. Another problem with this configuration is that the excess length portion, which can be drawn out from the container, cannot be made very long.